


Kiss me under the mistletoe

by Osamuskittycat



Series: Boywife Osamu AU [2]
Category: Haikyuu!!
Genre: Age Difference, Boywife Osamu, Feminization, M/M, Sex Toys, Sibling Incest, miyacest, older Atsumu, reference to future group sex
Language: English
Status: Completed
Published: 2020-12-27
Updated: 2020-12-27
Packaged: 2021-03-10 18:48:17
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 4,019
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28361937
Author URL: https://archiveofourown.org/users/Osamuskittycat/pseuds/Osamuskittycat
Summary: Osamu’s first Christmas since moving in with Atsumu is about to be a very special experience.
Relationships: Miya Atsumu/Miya Osamu
Series: Boywife Osamu AU [2]
Series URL: https://archiveofourown.org/series/2077527
Comments: 9
Kudos: 168





	Kiss me under the mistletoe

**Author's Note:**

> Happy holidays y’all. Have this absolute filth as my gift to you.

Christmas has always been one of Osamu’s favorite holidays despite the fact that he doesn’t really have a reason to celebrate it but Atsumu has always been very supportive of Osamu’s love for Christmas and never denied his baby brother anything that came with the holiday, from buying a real Christmas tree every year, to helping his baby brother decorate every inch of the house with Christmas decorations. 

But after Atsumu’s signing with Jackals and subsequent moving out, Osamu’s usual holiday cheer had died down since his favorite person to spend the holiday with was no longer home to help him decorate and sing Christmas songs, Osamu was left to sit and watch his favorite holiday movies alone without his big brother to keep him company. 

That was the case until Atsumu managed to convince their parents to allow Osamu to move in with him under the guise of his apartment being closer to Osamu’s new school and that they needed a vacation. 

December marked the third month of Osamu living with Atsumu, the duo instantly having fallen into a routine that they both enjoyed and found comfort in. 

Which was why Osamu didn’t grumble too much when Atsumu got up extra early for practice, leaving his little brother wrapped up in their blanket while he went around their apartment getting ready for his day. 

Just before Atsumu leaves for the gym, he drops a kiss to Osamu’s head, making the younger boy smile softly as he sits up a little to claim his older brother’s lips in a quick kiss. 

“Have fun at practice, I’ll make your favorite dinner tonight.”

Atsumu chuckles softly as he brushes his thumb across Osamu’s cheek before moving to grab his duffle. 

“I’m actually taking you out today after practice, Baby boy. We have to go shopping for decorations.”

Osamu blinks his eyes at Atsumu, who laughs at how confused his little brother looks. 

“Christmas is in a week, Baby. Did you really forget? We’ve gotta keep the tradition alive, especially now that you and I have this whole place to ourselves.”

Osamu’s heart beats wildly in his chest as he slowly processes Atsumu’s words, had he really forgotten about Christmas and their tradition? 

“Maybe we can get matching Christmas pajamas this year too! I’m thinking Mr and Mrs Clause style, cause you’re my little wifey.”

Atsumu’s brow wiggle cuts the seductive way he murmured ‘wifey’ against Osamu’s lips, the younger of the two snorting at his brother’s antics. 

“Please go to practice, Sumu-nii.”

Osamu has to kiss Atsumu’s pout before gently pushing him away with a laugh so that he can get ready for school now that he’s fully awake. 

“This isn’t over, Baby boy! Make sure you’re ready for a day full of holiday cheer later!”

—

The entire day at school sees Osamu in a daze, thinking about all the ways he and Atsumu could decorate their apartment. He has images of gold ribbons, glitter ornaments hanging from a beautifully dark green tree and Atsumu’s bright smile as he tries to convince Osamu to put a volleyball ornament on top of the tree instead of a star. 

To say the least, he’s extremely excited for his outing with Atsumu later. 

When Atsumu arrives to pick up Osamu from school, his sleek black sports car causing all of Osamu’s school mates to stare in awe as they always do whenever Atsumu shows up to pick Osamu up from school. 

The whispers tho, are always the funniest part in Osamu’s opinion. 

“Oh my...That’s Miya-san’s big brother!”

“I wish my brother was as cool as Miya’s brother!”

“I wish I was old enough to date him.”

Osamu had to refrain from flipping a few people off on his way to where Atsumu was leaning against his car with his classic Miya Atsumu grin plastered across his handsome face. 

“You’re such a show off.”

“Missed you too, Baby boy.”

—

Shopping with Atsumu proves to be the funnest and most exhausting experience Osamu has only ever felt a few times; after playing volleyball with his brother and after a few rounds of very intense sex that usually leaves him with jelly legs and marks all over his skin. 

“Hey, Baby boy! Check this out.”

Osamu lifts his head from where he was checking that he and Atsumu had all their bags, to see his brother pointing at a lingerie shop’s display of a ‘sexy’ Mrs Clause babydoll with matching stockings and hat. 

“How about I buy-“

“Absolutely not.”

“But-“

“I’ll send all your bentos to Bokun if you ask again.” 

Atsumu’s mouth clicks shut before he picks up the bags and makes his way towards the mall’s exit. 

“You’re evil, Baby boy.”

“I learned from the best, didn’t I?”

“Touché.”

—

It’s two days later, long after Osamu and Atsumu have set up the decorations and tree, successfully turning their apartment into a winter wonderland that always brings a smile to Osamu’s face anytime he sees all the little details he and Atsumu worked hard on. 

Osamu’s favorite little thing is of course the sparkly volleyball ornament that Atsumu found and placed on top of their tree. 

The only problem Osamu now is the lack of a proper Christmas gift for Atsumu, who somehow managed to buy enough gifts for Osamu that take up all the space under their tree. 

Osamu has brought his brother a bunch of little gifts but somehow he really wants to give the man who has always gone above and beyond for Osamu’s happiness, something more. But unfortunately for Osamu, he’s currently drawing up blank after blank. 

It’s not until later when catches sight of a tiny red bag from his favorite online sex shop hidden under their bed, probably another gift from Atsumu that he forgot to wrap, that an idea strikes him instantly. 

Osamu grabs his laptop off his bedside and quickly gets onto the website for the sex shop, a wide grin curling his lips when he finds what he’s looking for still in stock and a few extra pieces to add to the whole gift to make it extra special for his Sumu-nii. 

With a final click to make sure the package arrives two days later, Osamu gets up to make dinner for himself and Atsumu with a pep in his step and the perfect Christmas gift for his big brother. 

Osamu can’t wait to see the look on Atsumu’s face when he ‘unwraps’ his gift on Christmas Day...it’s going to be the best Christmas ever.

  
__

Osamu’s package arrives two days later, the bright red box inside of the plain brown shipping package makes Osamu’s hands shake with excitement as he carefully lifts it out and sets it on the bed. 

Osamu doesn’t have school due to the weather but Atsumu still has a team meeting, which gives Osamu enough time to go through everything and make sure he hides it all somewhere Atsumu won’t look. 

The Mrs Claude inspired babydoll is absolutely stunning and fits like a glove, the matching stockings doing wonders for Osamu’s legs. 

There’s a glittery red plug with a heart shaped base and a set of gold circular barbell nipple piercings that make Osamu blush brightly when he remembers just how easily turned on he gets anytime he puts his piercings back in. 

Taking one final look at himself in the mirror, Osamu smiles brightly as he does a little twirl in his matching red heels. The entire outfit is a success and Osamu really can’t wait to see the look on Atsumu’s face when he puts it all together again. 

—

Christmas Day rolls in and Osamu is awoken by his older brother jumping onto their bed, Atsumu’s larger frame caging Osamu under him as he smiles widely down at his little half-wake brother, “It’s Christmas, ‘Samu! Come on, you’ve got gifts to open!”

While Osamu was sure he liked Christmas more than his brother, it seemed that Atsumu was the more excited one this year which made Osamu laugh softly as he leaned up to kiss Atsumu softly before crawling out from under him, “You’re acting like this is your first Christmas.”

Atsumu’s wide grin softens into a sweeter smile, one that Osamu knows is reserved just for him, “I’m just really happy that I get to spend it with you this year. I know it’s been awhile since I left home and all that but now it’s just you and me...together in our own little place.”

Osamu’s heart swells as he sits on his knees, hands reaching out for Atsumu’s face to pull him into a deep kiss that leaves his older brother chasing his retreating lips the second he pulls away, “I love you, Sumu-nii.”

There’s so much love in Atsumu’s eyes that Osamu has to close his own before he’s overwhelmed by how much his older brother loves him back. 

“I love you too, Baby boy. Now let’s get going, we’ve got gifts to unwrap.”

—

Osamu can’t believe all the unwrapped gifts surrounding him as he sits on Atsumu’s lap, absolutely showering his Sumu-nii in kisses while hugging him close, causing his brother to laugh softly at his antics. 

“You’re welcome, Baby boy. I love you too, a thousand times over.”

Osamu fights back a sniffle as he moves to rest his forehead against Atsumu’s, a soft smile taking over his face as he nudges their noses against each other’s, “You spoil me too much, Sumu-nii.”

That makes Atsumu snort softly as he rubs his hands up and down Osamu’s sides, the diamond stud in his ear that Osamu picked out for him, glittering thanks to the tree’s multiple lights.

“I don’t think I spoil you enough, Baby boy.”

Osamu opens his mouth to argue but Atsumu stops him with a kiss to the tip of his nose, grinning at Osamu’s annoyed pout. 

“Anyway, where’s this super secret gift of yours? I’ve been dying to figure out what it is since you told me to not look at my bank statement.” 

Osamu shakes his head fondly as he gently pulls Atsumu’s hands off his hips, kissing him softly before he gets off of his brother’s lap completely. 

“I need a few minutes to get it together, can you throw out the wrapping paper while I get it together?” 

The curious look on Atsumu’s face makes Osamu bite back a giggle as he snags the new red bottoms Atsumu brought for him off the floor and races off to their room, calling a cheerful ‘No peeking!’ over his shoulder before shutting and locking the door to the bedroom. 

Hidden deep under their bed is a plain brown box that contains all of Atsumu’s gifts and Osamu is absolutely buzzing with excitement as he pulls it out to begin putting everything together in the master bathroom. 

After a quick wash, Osamu manages to slip the plug in without issue but the sensation never stops making him desperate for more but he forces himself to focus on putting the new piercings in before sliding the lacy red stockings up his legs, clipping them to his garter belt. 

Osamu can’t believe the sight of himself in the mirror but he’s enjoying all of it, especially when he finally slips on the babydoll after he’s finished his makeup, the mascara making his grey eyes pop. 

The brand new red bottoms follow last, the soft click of the heel against the floor as Osamu walks out of the bathroom makes him feel powerful beyond words, the sight of him in the mirror only adding more to the fire burning inside of him. 

Atsumu’s soft call from outside the bedroom snaps Osamu out of his head, “You okay in there, Baby?”

Osamu laughs softly to himself as he runs a hand through his hair, happy that it has gotten longer since he and started dating, “I’m fine. Wait for me in the living room please, I’ll bring your surprise out in a second.”

“Okay, okay, I’m going”

Once Osamu is sure that Atsumu is done he takes in a deep breath and slowly opens the door, feet slowly moving over the floor so as to not alert Atsumu of what his gift is just yet, “Close your eyes, Sumu-nii.”

Atsumu laughs softly as he calls back a soft, “Yes, Baby.” that makes Osamu’s heart rate pick up a little as he peeks around the door frame to see Atsumu with his hands over his eyes, the sight so endearing that Osamu wishes he could snap a picture but he just takes in another deep breath before moving to stand in front of Atsumu.

Brushing his hands over his outfit one last time, Osamu squares his shoulders and smiles brightly before telling Atsumu to open his eyes, “You can look now, Sumu-nii.” 

If there was a way to engrave the image of someone into his memory forever, Osamu would choose the image of Atsumu staring at him like he’s some precious piece of artwork, hazel eyes wide as they trail all over Osamu’s body.

“B-Baby...You look spectacular.”

Osamu blushes as he shyly toys with the ribbon near the top of his outfit, a soft gasp slipping from his mouth when Atsumu gets up and crowds into his space, leaving no room between them as Atsumu’s hands lift to rest on Osamu’s hips. 

“Fuck. This is the best gift ever, Princess. I can’t believe you actually brought this little number just for me, Sumu-nii is one lucky bastard.”

Osamu accepts the bruising kiss Atsumu lays on him, toes curling as he tries to push up for more but then Atsumu pushes him away, grabbing his hand to twirl him around to see the entire outfit in all its glory. 

“Damn. Lucky bastard is an understatement,” Atsumu smirks as swoops in to press a kiss under Osamu’s ear, making the poor boy whimper softly, “I’ve been blessed by some god to have you be mine, Princess.”

Osamu’s glossy lips part on a soft gasp at how sincere his Sumu-nii looks, the heat in his eyes making Osamu’s legs weak which causes him to grip onto his older brother’s shirt for support as he pushes up to kiss the daylights out of Atsumu, who crouches down to hoist Osamu up until he can wrap his legs around his brother’s waist. 

Atsumu’s hands grope Osamu’s ass the whole way to their bedroom which causes his baby brother to whimper against his mouth while trying to pull Atsumu’s Christmas sweater off at the same time. 

“Shh. Easy there, Princess. You’re my gift to unwrap, aren’t you?” At Osamu’s nod, Atsumu grins while kicking the door to their bedroom open, “Then just relax and let me unwrap my gift at my own pace...I wanna enjoy every single last bit of it.”

The moment Osamu’s back hits the mattress, he knows he’s in for a very long night. 

—

“S-Sumu-nii! Please!” 

Osamu has no idea how long he’s been begging for Atsumu to have mercy on him but his older brother seems very preoccupied with eating out Osamu’s little hole like a man starving to care about his begging. 

“P-Please...I want S-Sumu-nii’s cock.”

A third finger joins the two already pressed up deep inside of him while Atsumu continues to make Osamu as wet as possible, his dark chuckles sending vibrations through Osamu’s.

“Not yet, Princess.” 

Is all Osamu gets before Atsumu goes back to stretching him open, despite having fucked Osamu with the plug just minutes prior but he had made a comment about wanting Osamu’s hole to be gaping by the time he was done with his baby. How he wanted to see his come drip out of Osamu’s hole before he shoved the plug back inside to keep all of Sumu-nii’s cum inside. 

His nipples ached from Atsumu sucking on them while rutting his cock against Osamu’s thigh, teasing his little brother about how beautiful his tits were, how all the girls in his class must be jealous of his pretty little tits. 

The new piercing had only added more fuel to Atsumu’s fire, his fingers plucking at the sensitive buds from time to time while he made himself at home between Osamu’s legs, it was a sensation overload like nothing Osamu had ever felt before. 

“Does my baby really want Sumu-nii’s cock that bad? You want me to fill your little hole with my cum until it’s leaking out of you?” 

Atsumu’s mouth is going to be the end of Osamu in more ways than one, he’s absolutely sure of it, “You want me to get your other toy too? Wanna take two cocks at once like a big boy?”

Osamu can only nod, head bobbing quickly as he throws an arm over his eyes, completely overwhelmed by Atsumu’s words and the way his fingers are moving relentlessly against his prostate causing stars to dance in Osamu’s head. 

“P-Please...”

A soft kiss is pressed to Osamu’s lips before the warmth is gone, leaving him to just lay there and take whatever Atsumu has in store for him. Because that’s what good boys do.

—

The feeling of two cocks pressed up inside of him makes Osamu’s brain shut down, eyes fluttering and body shaking as he tries to get a grip on his surroundings but the only thing he can do is hyper focus on the way his big brother is holding him close to his chest while fucking him stupid. 

“You should see how you look in this mirror right now, Baby. An absolute dream to look at. Taking Sumu-nii’s cock and your toy together so well, it’s like you were born for this.” 

Osamu’s moan breaks off into sob as Atsumu sets a mind melting rhythm by fucking in while pulling the toy out before the cycle continues. 

“I bet you’re imagining what it would be like if the second cock inside of you was real...I wonder if that cock belongs to someone I know.”

The scream that rips out of Osamu when Atsumu shoves both his cock and the dildo into his little brother’s hole, is muffled against Atsumu’s neck while the younger boy shakes in his arms. 

“It’s okay, Princess...I know you’re a little slut, who wouldn’t mind if I shared your little hole with my friends. You’d love it if I invited Shoyo-kun and Bokkun to come over and fuck your little hole until it was absolutely ruined, your little tummy bulging from all the cum they’d fuck into you.”

Osamu has only ever mentioned it in passing that he thought his brother’s teammates were hot but he didn’t think Atsumu would even think about sharing him like that, his brother had always been clear about the fact that Osamu belonged to him and him only. 

“P-Please! I-I want...I want to be their little cum dump, Sumu-nii! W-Wanna be a good boy for them too!”

Atsumu curses under his breath as he pulls the dildo out of Osamu, making the poor boy whine before it breaks off into a shriek when Atsumu flips his baby brother until he’s face down into the bed, hips smacking loudly against Osamu’s ass every time he fucks into him. 

“I’ll think about sharing you.” The smack that lands on Osamu’s ass is so loud despite their heavy breathing, the sting making Osamu’s cock leak against the sheets, “You’re my little Princess, I make the rules.”

“W-Whatever Sumu-nii wants! I’ll do whatever Sumu-nii wants! I’ll be the best boy ever!” 

Lips press softly against the back of Osamu’s neck as Atsumu’s movements slowly start to lose their rhythm, “I know you will be, Princess. Because my sweet little baby always does so good for me, my gorgeous wifey.”

Osamu’s mantra of ‘I love you’ doesn’t stop despite him being so worn out, having already come untouched just by the way Atsumu spoke to him but doesn’t beg for his big brother to stop, just leans forward to give Atsumu better sight of where his cock is fucking into Osamu’s ruined hole. 

“I-I want Sumi-nii’s cum...wanna be a good cock sleeve for my Sumu-nii.”

The absolute filth falling from Osamu’s mouth makes Atsumu’s orgasm hitting him full throttle, pressing his teeth into his baby brother’s shoulder as he fills his wifey’s tiny little hole with his cum, “Gods...you’re such a good boy for me, Samu.” 

Osamu blushes brightly as Atsumu slowly pulls out of him, hands holding his cheeks apart to see Osamu’s ruined hole flutter because of the cool air, the small dribble of cum that slips out makes Atsumu smirk as he reaches for the red plug to shove it deep into his baby brother before smacking his ass just to hear Osamu whimper.

“Who knew my little Princess wanted to be the team’s personal cum dumb, I bet you’d make all those guys happy with your slutty little holes. A personal cocksleeve for them to use any which way I wanted, isn’t that right, Osamu? Tell me the truth, Princess.”

Osamu’s head feels fuzzy as he’s turned onto his back, staring up at Atsumu with tear stained cheeks and a flush that runs all the way across his body, “I-I’m Sumu-nii’s c-cocksleeve...B-But I want to play with Sumu-nii’s f-friends too. Please? I’ll be such a g-good boy.”

The soft coo that leaves Atsumu’s lips makes a shiver run down Osamu’s spine as he watches his older brother scoop up the mess of cum from between his legs before lifting his hand up towards Osamu’s mouth, causing the boy to whine as he suckles on his older brother’s fingers. 

“I know you’ll be such a good boy, I’m so proud of my little Princess being the sweetest thing ever. I just gotta wonder how my teammates will react when they find out just how much of a needy little whore their favorite little cheerleader is.”

Osamu whimpers around Atsumu’s fingers, legs spread open as his older brother’s other hand teasingly runs along the inside of his thigh before calloused fingers wrap around his over sensitive cock but Osamu can’t move away from Atsumu’s touch, he feels drunk with the desperate need for more. 

His big brother was right, Osamu was a little cum slut who couldn’t just be satisfied with just one cock in his little hole, he needed more...he wanted his Sumu-nii to share him with his teammates, wanted to be ruined by the people he’d grown to admire. 

All Osamu could think of now as Atsumu reached for the remote for his plug was which of his brother’s teammates would show him no mercy in bed and who would enjoy fucking his throat the most. 

He really was nothing more than a little cockslut, a cumdump for his big brother and hopefully his brother’s teammates if Atsumu felt generous enough to share him with his friends. 

The plug inside of hun is amped up to the highest setting, a broken scream ripping its way out of Osamu’s throat before it’s muffled by Atsumu slowly pressing his semi-hard cock into Osamu’s mouth. 

“Shh, Princess...Just let Sumu-nii take care of you right now and then we’ll talk about what to do about getting the boys to come over so you can show them what a good little whore you are.”

Osamu can’t help but smile around his Sumu-nii’s cock, turning until he’s wrapped around his brother’s leg so he can keep his cock nice and warm in his throat while he takes a quick nap. 

Atsumu may have spoiled his little brother a lot this Christmas but he doesn’t mind spoiling him a little bit more and he’s sure his teammates want to do the exact same as him. 

Atsumu really can’t wait to see the look on his Princess’s face when all the boys come over on their day off to deliver Osamu their joint Christmas gift, his sweet baby is going to be absolutely ruined by the time everyone is done with him and Atsumu can’t wait to witness it all. 

Best Christmas ever. . 

  
  
  
  
  
  
  
  
  


**Author's Note:**

> Follow me on Twitter for more of this: osamuskittycat


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